diseases which are commonly associated with lepto,” says Linton. There seems to be a genetic component to susceptibility to ERU---the disease is more prevalent in Appaloosas than in other breeds.
When it affects the uterus of a pregnant mare, leptospirosis can cause abortion late in gestation. “And since lepto abortions are likely underreported---meaning a definitive diagnosis was not made---we probably underestimate how significant a problem this is,” says Grenager. In some cases, the foal may be born alive but very sick with leptospirosis. “The fetal fluids and placental fluids are infective,” says Linton. “If another horse comes into contact with these fluids this is another way the disease can be transmitted.”
Kidney disease from leptospirosis isn’t common in horses, but some do develop acute renal failure. A kidney infection may result in shedding of the pathogen via urine. “Even after the infection is under control, the horse may continue to shed bacteria for several weeks,” Linton says. “Since the bacteria can be passed in the urine, it’s important to isolate any horse with an active kidney infection.”
If the leptospirosis is still in the acute stage of infection, your veterinarian will treat it with the appropriate antibiotic. “There are different antibiotic recommendations based on the body system that the bacteria happens to be affecting,” says Gilsenan. “Your veterinarian will recommend the appropriate treatment.”
Likewise, other treatments will depend on the body system affected. For example, says Grenager, “a horse with kidney failure will also need supportive care and lots of fluids.” Treatment cannot help a mare who has already aborted, but affected foals born alive may respond to antibiotics. In both cases, the horses may need to be kept isolated for up to 16 weeks with periodic tests to make sure they are not shedding bacteria in their urine.
ERU is difficult to treat effectively because it is more than just a simple bacterial infection---the disease, which can appear two to eight months after the initial leptospirosis infection, is an autoimmune disorder. Although how Leptospira organisms cause ERU isn’t fully understood, it appears that the proteins on L. pomona are similar enough to proteins found in the tissues within the eye to cross-react with the antibodies. In other words, the antibodies created to fight the pathogen end up attacking the body’s own tissues as well.
“One of the things that complicates therapy is that often it’s not simply the organism that causes a problem but rather the animal’s immune response to the organism, such as when an eye is damaged,” says Gilsenan. “Part of the treatment involves quieting down the inflammation in the eye with some kind of corticosteroid, and another component is using an antibiotic that will penetrate into the eye.”
• Vaccinate. In late 2015, Zoetis introduced the first vaccine against leptospirosis approved for use in horses. “The new vaccine has only been out for a short time, but Zoetis did rigorous safety trials and an efficacy trial that showed it works,” says Grenager. “It is labeled as effective against L. pomona.”
In controlled trials, the vaccine prevented leptospiremia---the presence of the bacteria in the bloodstream--after initial exposure. It is believed that reducing the infection in the bloodstream reduces the risk of the complications associated with leptospirosis---ERU, kidney disease or abortion.
• Adjust management practices to minimize exposure. “It is better to not feed hay on the ground. It also helps if you can minimize areas of standing water, which is helpful in preventing many other problems as well,” says Grenager. Keep water troughs and buckets clean, and fence off access to ponds, marshy areas and other natural water sources.
“If a mare aborts, you need to test for lepto and if the test is positive, treat and isolate her until proven that she is no longer shedding bacteria,” Grenager says. “All the aborted tissues should be removed and the area disinfected appropriately.”
A common cause of diarrhea in mature horses, salmonellosis is caused by Salmonella enterica bacteria. The most frequent method of transmission for salmonella is fecal-to-oral, meaning that the bacteria are shed in manure, then consumed with contaminated feed or water. Strictly speaking, salmonellosis isn’t solely a water-borne disease, but it is passed easily through contaminated water---both in unclean buckets and troughs as well as natural ponds and streams.
“Salmonella can be readily transmitted via water or human hands and boots,